1. Field of Invention
This invention pertains to forming boards for a paper making apparatus and more particularly to forming boards which decrease the flocculation of the stock used to form paper.
2. Description of the Prior Art
In the early practice of the art of making paper by hand, the vatman scooped up stock from a vat by means of a mold and then gave the mold a series of shakes or "strokes" while water drained out of the mold. The paper sheet which was formed was very homogenous. Paper manufacturers today using automated machinery strive to obtain a paper sheet which is comparable in uniformity, however most papers manufactured by automatic means lack uniformity. Modern studies have shown that one of the reasons for this lack of uniformity is flocculation of the stock not only in the headbox but also during the relatively short period of time spent by the stock while it is on the forming fabric but before it is formed. This flocculation has been somewhat reduced by the use of rectifier rolls inside the headbox, and transversal shakers disposed under the forming fabric. It has been found however that as the speed of the fabric is increased, these methods become less effective. It appears that the vatman's stroke dispersed the flow of stock by inducing therein complex shears, and that in order to produce high-quality paper at high speeds, new means must be found for emulating the stroke at high speeds.
Several methods have been suggested for breaking up the flocs deposited or formed on the forming fabric, by creating a turbulence in the stock. For example the Sepal U.S. Pat. No. 3,573,159 and Johnson U.S. Pat. No. 3,874,998 have suggested forming boards having transversal channels for creating transversal waves extending across the fabric. However these methods were still found to be insufficient.
Recently Otto J. Kallmes and Manuel Perez have suggested the successive generation and destruction of waves which extend longitudinally with respect to the forming fabric as an effective deflocculation means for high speed papermaking machines. This type of action forces relatively large transversal movement of stock during the forming process due to transversal shear thus breaking up and/or limiting the formation of flocs therein. Messrs. Kallmes and Perez' work was described at the 1982 Papermakers Conference, and published by TAPPI.